1. Field of the Invention
The present invention relates to a continuous blood-pressure monitor apparatus which continuously monitors blood pressure of a living subject based on a pressure pulse wave detected by a pressure-pulse-wave sensor, and particularly to the art of appropriately pressing the pressure-pulse-wave sensor against an artery of the subject via body surface of the subject.
2. Related Art Statement
U.S. Pat. No. 5,762,610 discloses a continuous blood-pressure (xe2x80x9cBPxe2x80x9d) monitor apparatus which continuously monitors the BP of a living subject. This BP monitor apparatus includes (a) a pressure-pulse-wave (xe2x80x9cPPWxe2x80x9d) sensor which includes a plurality of pressure sensing elements which are arranged in a reference direction and each of which detects a PPW propagated thereto from an arterial vessel of the subject and produces a PPW signal representing the detected PPW that includes a plurality of heartbeat-synchronous pulses, the PPW sensor having a press surface which supports the pressure sensing elements arranged in the reference direction and which is adapted to be pressed against the arterial vessel via a body surface or skin of the subject such that the arranged pressure sensing elements intersect the arterial vessel; (b) a pressing device which presses, with a pressing force, the PPW sensor against the arterial vessel via the body surface; (c) optimum-element selecting means for selecting, as an optimum element, one of the pressure sensing elements that provides the detected PPW including a heartbeat-synchronous pulse whose amplitude is greatest of respective amplitudes of respective heartbeat-synchronous pulses of the detected PPWs provided by the pressure sensing elements; (d) optimum-pressing-force determining means for changing the pressing force of the pressing device and determining, based on the PPW detected by the optimum element while the pressing force is changed, an optimum pressing force with which the pressing device presses the PPW sensor against the arterial vessel via the body surface such that a portion of a wall of the arterial vessel is substantially flattened; (e) optimum-pressing force maintaining means for maintaining the optimum pressing force of the pressing device; and (f) estimated-BP determining means for determining an estimated BP value according to a predetermined relationship between BP and magnitude of PPW, based on a magnitude of each of a plurality of heartbeat-synchronous pulses of the detected PPW represented by the PPW signal produced by the optimum element in a state in which the PPW sensor is pressed against the arterial vessel with the optimum pressing force maintained by the optimum-pressing-force maintaining means. The BP monitor apparatus monitors the BP of the subject by successively determining the estimated BP values of the subject.
The estimated BP values successively determined by the above BP monitor apparatus cannot accurately reflect actual BP values of the subject unless the PPW sensor is appropriately pressed against the arterial vessel via the body surface such that a portion of the wall of the artery is substantially flattened. However, the prior BP monitor apparatus does not display the optimum pressing force of the pressing device determined by the optimum-pressing-force determining means, or displays the optimum pressing force alone. Therefore, it is difficult for an operator who operates the prior BP monitor apparatus to judge, from what is displayed thereby, whether the optimum pressing force has been determined in an appropriate state in which a portion of the wall of the artery is stably flattened and accordingly the appropriate state can last for a long time, or in an inappropriate state in which a portion of the wall of the artery is considerably unstably flattened and accordingly the state in which the portion of the wall of the artery is flattened cannot last for so long a time.
It is therefore an object of the present invention to provide a blood-pressure monitor apparatus which assures that an operator can recognize how the apparatus presses an arterial vessel of a living subject at the time of determination of an optimum pressing force.
(1) According to a first feature of the present invention, there is provided a blood-pressure monitor apparatus for monitoring a blood pressure of a living subject, comprising a pressure-pulse-wave sensor which includes a plurality of pressure sensing elements which are arranged in a reference direction and each of which detects a pressure pulse wave propagated thereto from an arterial vessel of the subject and produces a pressure-pulse-wave signal representing the detected pressure pulse wave that includes a plurality of heartbeat-synchronous pulses, the pressure-pulse-wave sensor having a press surface which supports the pressure sensing elements arranged in the reference direction and which is adapted to be pressed against the arterial vessel via a body surface of the subject such that the arranged pressure sensing elements intersect the arterial vessel; a pressing device which presses, with a pressing force, the pressure-pulse-wave sensor against the arterial vessel via the body surface; optimum-element selecting means for selecting, as an optimum element, one of the pressure sensing elements that provides the detected pressure pulse wave including a heartbeat-synchronous pulse whose amplitude is greatest of respective amplitudes of respective heartbeat-synchronous pulses of the detected pressure pulse waves provided by the pressure sensing elements; optimum-pressing-force determining means for changing the pressing force of the pressing device and determining, based on the pressure pulse wave detected by the optimum element while the pressing force is changed, an optimum pressing force with which the pressing device presses the pressure-pulse wave sensor against the arterial vessel via the body surface such that a portion of a wall of the arterial vessel is substantially flattened; optimum-pressing-force maintaining means for maintaining the optimum pressing force of the pressing device; estimated-blood-pressure determining means for determining an estimated blood pressure according to a predetermined relationship between blood pressure and magnitude of pressure pulse wave, based on a magnitude of each of a plurality of heartbeat-synchronous pulses of the detected pressure pulse wave represented by the pressure-pulse-wave signal produced by the optimum element in a state in which the pressure-pulse-wave sensor is pressed against the arterial vessel with the optimum pressing force maintained by the optimum-pressing-force maintaining means; and an amplitude-change-curve displaying device which displays, in a two-dimensional coordinate system having a first axis indicative of pressing force and a second axis indicative of amplitude of heartbeat-synchronous pulse of pressure pulse wave, an amplitude-change curve representing a change of the respective amplitudes of the heartbeat-synchronous pulses of the pressure pulse wave detected by the optimum element, with respect to a change of the pressing force of the pressing device caused by the optimum-pressing-force determining means.
According to this feature, the amplitude-change-curve displaying device displays the amplitude-change curve representing the change of the respective amplitudes of the heartbeat-synchronous pulses of the pressure pulse wave detected by the optimum element, with respect to the change of the pressing force of the pressing device caused by the optimum-pressing-force determining means. Therefore, an operator who operates the present BP monitor apparatus can recognize how the apparatus presses the arterial vessel of the subject at the time of determination of the optimum pressing force.
(2) According to a second feature of the present invention that includes the first feature (1), the blood-pressure monitor apparatus further comprises an estimated blood-pressure displaying device which displays the estimated blood pressure determined by the estimated-blood-pressure determining means.
(3) According to a third feature of the present invention that includes the first or second feature (1) or (2), the blood-pressure monitor apparatus further comprises an optimum-pressing-force displaying device which displays, in the two-dimensional coordinate, system in which the amplitude-change curve is displayed, a symbol representing the optimum pressing force determined by the optimum-pressing-force determining means. According to this feature, the operator can judge whether the optimum pressing force has been determined at an appropriate pressing force.
(4) According to a fourth feature of the present invention that includes any one of the first to third features (1) to (3), the blood-pressure monitor apparatus further comprises judging means for judging, based on the pressure pulse wave detected by the optimum element while the pressing force is changed by the optimum-pressing-force determining means, whether the pressing device appropriately presses the pressure-pulse-wave sensor against the arterial vessel via the body surface. According to this feature, the judging means can identify an inappropriate state in which a space is left between the PPW sensor and the body surface because the arterial vessel is too shallow under the body surface and accordingly the optimum pressing force determined by the optimum-pressing-force determining means is too small, and an inappropriate state in which the PPW sensor cannot be pressed with a sufficiently great pressing force because the artery is too deep under the body surface and accordingly the optimum pressing force determined by the optimum-pressing-force determining means is too great to be applied by the pressing device. Thus, the present BP monitor apparatus can automatically judge whether the state in which the PPW sensor is pressed against the artery is appropriate.
(5) According to a fifth feature of the present invention that includes any one of the first to fourth features (1) to (4), the blood-pressure monitor apparatus further comprises a blood-pressure measuring device which includes an inflatable cuff adapted to be wound around a body portion of the subject and measures at least one blood pressure value of the subject based on a pulse wave transmitted to the cuff while an air pressure in the cuff is changed; and a relationship determining means for determining the relationship between blood pressure and magnitude of pressure pulse wave, based on the at least one blood pressure value measured by the blood-pressure measuring device and at least one magnitude of a heartbeat-synchronous pulse of the pressure pulse wave detected by the optimum element in the state in which the pressure-pulse-wave sensor is pressed against the arterial vessel with the optimum pressing force maintained by the optimum-pressing-force maintaining means.
(6) According to a sixth feature of the present invention, there is provided a blood-pressure monitor apparatus for monitoring a blood pressure of a living subject, comprising a pressure-pulse-wave sensor which includes a plurality of pressure sensing elements which are arranged in a reference direction and each of which detects a pressure pulse wave propagated thereto from an arterial vessel of the subject and produces a pressure-pulse-wave signal representing the detected pressure pulse wave that includes a plurality of heartbeat-synchronous pulses, the pressure-pulse-wave sensor having a press surface which supports the pressure sensing elements arranged in the reference direction and which is adapted to be pressed against the arterial vessel via a body surface of the subject such that the arranged pressure sensing elements intersect the arterial vessel; a pressing device which presses, with a pressing force, the pressure-pulse-wave sensor against the arterial vessel via the body surface; optimum-element selecting means for selecting, as an optimum element, one of the pressure sensing elements that provides the detected pressure pulse wave including a heartbeat-synchronous pulse whose amplitude is greatest of respective amplitudes of respective heartbeat-synchronous pulses of the detected pressure pulse waves provided by the pressure sensing elements; optimum-pressing-force determining means for changing the pressing force of the pressing device and determining, based on the pressure pulse wave detected by the optimum element while the pressing force is changed, an optimum pressing force with which the pressing device presses the pressure-pulse wave sensor against the arterial vessel via the body surface such that a portion of a wall of the arterial vessel is substantially flattened; optimum-pressing-force maintaining means for maintaining the optimum pressing force of the pressing device; estimated-blood-pressure determining means for determining an estimated blood pressure according to a predetermined relationship between blood pressure and magnitude of pressure pulse wave, based on a magnitude of each of a plurality of heartbeat-synchronous pulses of the detected pressure pulse wave represented by the pressure- pulse-wave signal produced by the optimum element in a state in which the pressure-pulse-wave sensor is pressed against the arterial vessel with the optimum pressing force maintained by the optimum-pressing-force maintaining means; and a signal-magnitude-change-curve displaying device which displays, in a two-dimensional coordinate system having a first axis indicative of pressing force and a second axis indicative of magnitude of pressure-pulse-wave signal, a signal-magnitude-change curve representing a change of respective magnitudes of respective predetermined periodic points of the heartbeat-synchronous pulses of the detected pressure pulse wave represented by the pressure-pulse-wave signal produced by the optimum element, with respect to a change of the pressing force of the pressing device caused by the optimum-pressing-force determining means.
According to this feature, the signal-magnitude-change-curve displaying device displays the signal-magnitude-change curve representing the change of respective magnitudes of respective predetermined periodic points of the heartbeat-synchronous pulses of the detected PPW represented by the PPW signal produced by the optimum element, with respect to the change of the pressing force of the pressing device caused by the optimum-pressing-force determining means. Therefore, an operator who operates the present BP monitor apparatus can recognize how the apparatus presses the arterial vessel of the subject at the time of determination of the optimum pressing force.
(7) According to a seventh feature of the present invention that includes the sixth feature (6), the blood-pressure monitor apparatus further comprises an estimated-blood-pressure displaying device which displays the estimated blood pressure determined by the estimated-blood-pressure determining means.
(8) According to an eighth feature of the present invention that includes any one of the sixth or seventh feature (6) or (7), the blood-pressure monitor apparatus further comprises an optimum-pressing-force displaying device which displays, in the two-dimensional coordinate system in which the signal-magnitude-change curve is displayed, a symbol representing the optimum pressing force determined by the optimum-pressing-force determining means. According to this feature, the operator can judge whether the optimum pressing force has been determined at an appropriate pressing force.
(9) According to a ninth feature of the present invention that includes any one of the sixth to eighth features (6) to (8), the blood-pressure monitor apparatus further comprises judging means for judging, based on the pressure pulse wave detected by the optimum element while the pressing force is changed by the optimum-pressing-force determining means, whether the pressing device appropriately presses the pressure-pulse-wave sensor against the arterial vessel via the body surface.
(10) According to a ninth feature of the present invention that includes any one of the sixth to ninth features (6) to (9), the blood-pressure monitor apparatus further comprises a blood-pressure measuring device which includes an inflatable cuff adapted to be wound around a body portion of the subject and measures at least one blood pressure value of the subject based on a pulse wave transmitted to the cuff while an air pressure in the cuff is changed; and a relationship determining means for determining the relationship between blood pressure and magnitude of pressure pulse wave, based on the at least one blood pressure value measured by the blood-pressure measuring device and at least one magnitude of a heartbeat-synchronous pulse of the pressure pulse wave detected by the optimum element in the state in which the pressure-pulse-wave sensor is pressed against the arterial vessel with the optimum pressing force maintained by the optimum-pressing-force maintaining means.